1. Field
It relates to a liquid crystal display device. In particular, it relates to a liquid crystal display such as a portable information terminal, which is equipped with a liquid crystal display device including a liquid crystal display protection panel and a liquid crystal module including a liquid crystal display (LCD) panel.
2. Description of the Related Art
Liquid crystal display devices have been widely used for display units of various electronic devices such as a portable information terminal such as a cell phone or a PDA (personal digital assistants), a portable PC (personal computer) such as a laptop PC, a desktop PC, and a television on account of being thin and lightweight as well as because of low-voltage driving and power-saving.
FIG. 1 is a front view of a conventional cell phone equipped with a liquid crystal display device.
A cell phone 10 of FIG. 1 includes a stationary-side case 1 and a movable-side case 3 coupled with the stationary-side case 1 through a hinge 2 in a foldable manner. In the illustrated example of FIG. 1, the movable-side case 3 of the cell phone 10 is opened.
The stationary-side case 1 has a flat, substantially rectangular shape. An inner surface 4 of the stationary-side case 1 is provided with, for example, plural push buttons 5, 6, and 7. Further, an inner surface 8 of the movable-side case 3 is provided with, for example, a liquid crystal display device 9.
FIG. 2 is a cross-sectional view of the liquid crystal display device 9 of FIG. 1.
As shown in FIG. 2, the liquid crystal display device 9 includes a front case 11, a rear case 12, and an LCD (liquid crystal display) protection panel 13.
The front case 11 is a molded case made of a resin or magnesium alloy, for example. A lower surface of the front case 11 is bonded to an upper end of the rear case 12 by means of claws or screws.
A liquid crystal display protection panel mounting surface 11a extends from an upper portion of the front case 11. The LCD protection panel 13 made of polymethyl methacrylate (PMMA) as an acrylic polymer is placed on the liquid crystal display protection panel mounting surface 11a through a double-faced adhesive tape 14, for example.
FIG. 3 is an enlarged view of a portion A enclosed by the dotted line of FIG. 2. As shown in FIG. 3, the liquid crystal display protection panel mounting surface 11a is a flat surface substantially parallel to the horizontal. An outer edge of the LCD protection panel 13 is fixed onto the liquid crystal display protection panel mounting surface 11a by the double-faced adhesive tape 14. Further, there is no space but a small gap resulting from dimensional tolerances, between an end face of the LCD protection panel 13 and an inner surface of the upper portion of the front case 11.
Referring back to FIG. 2, a concave liquid crystal module holder 16 having a substrate 15 attached to the bottom is provided inside the front case 11. Electronic components such as a chip capacitor are mounted onto the substrate 15 but are not illustrated in FIG. 2. Liquid crystal modules 17 and 18 are nested into the concave portion of the liquid crystal module holder 16. By the way, the liquid crystal module 18 is a liquid crystal display (LCD) panel, and the liquid crystal module 17 is a liquid crystal display (LCD) panel holder for holding the LCD panel 18.
An upper edge of the liquid crystal module holder 16 is in contact with a lower side of the upper portion of the front case 11. The liquid crystal module holder 16 supports the front case 11. Further, a dustproof gasket 19 made of cushioning such as urethane foam rubber is put on an upper edge of the liquid crystal module 18. The dustproof gasket 19 is in contact with a lower surface of the LCD protection panel 13. This structure protects the liquid crystal modules 17 and 18 from dust.
In addition, Japanese Laid-open Patent Publication No. 2004-111153 proposes a backlight and a liquid crystal display device, which include a light source supporting member for supporting a light source to a chassis or a corner portion of a light reflecting member, and in which a reflector is partially positioned between the chassis and the light source supporting member, and the light source supporting member controls movement of a front edge portion of the reflector relative to the chassis in a direction parallel to a front side of a light guide.
However, the structure of FIG. 2 involves the following problems. Referring to cross-sectional views of FIGS. 4A and 4B similar to FIG. 2, the problems are described below.
The LCD protection panel 13 tends to expand in the direction of the arrow of FIG. 4A due to temperature rise or moisture absorption. How much the LCD protection panel 13 extends due to the expansion resulting from moisture absorption varies depending on water absorption, a panel thickness, etc. If the LCD protection panel 13 is made of, for example, polymethyl methacrylate (PMMA) as an acrylic polymer, the water absorption is 0.3%.
On the other hand, as described above, the outer edge of the lower surface of the LCD protection panel 13 is fixed onto the liquid crystal display protection panel mounting surface 11a through the double-faced adhesive tape 14. Further, there is no space but a small gap resulting from dimensional tolerances, between the end face of the LCD protection panel 13 and the inner surface of the upper portion of the front case 11.
Therefore, although the LCD protection panel 13 tends to expand due to temperature rise or moisture absorption, the extension in a horizontal direction (direction of the arrow of FIG. 4A) resulting from the expansion is restricted.
As a result, as shown in FIG. 4B, the LCD protection panel 13 warps inwardly (downwardly in FIG. 4B) according to the expansion, and the lower surface of the LCD protection panel 13 comes into contact (interferes) with the upper surface of the LCD panel 18 in some cases. If the lower surface of the LCD protection panel 13 comes into contact with the upper surface of the LCD panel 18, the contact portion looks like a droplet infiltrated in a space between the LCD protection panel 13 and the LCD panel 18. As a result, there is no choice but to repair the liquid crystal display device 9.
One conceivable countermeasure against such a problem is to secure enough space between the lower surface of the LCD protection panel 13 and the upper surface of the LCD panel 18 not to bring the lower surface of the LCD protection panel 13 and the upper surface of the LCD panel 18 into contact with each other even if the LCD protection panel 13 expands. However, this structure leads to enlargement of the liquid crystal display device 9 and thus the cell phone 10.